Safety pilot



April 22, 1958 L. OHMAN 2,831,318

SAFETY PILOT Filed July 25, 1954 LACHLAN OHMAN BY W ATTORNEY 37 39 32 39 37 INVENTOR United States PatentO SAFETY PILOT Application July 23, 1954, Serial No. 445,370

6 Claims. (Cl. 60-25) The invention described herein relates to the combination of a pilot burner for a main burner and a flame sensing unit associated therewith for controlling a safety device that supplies fuel to the main burner. Such a combination is generally known in the heating controls art as a safety pilot. More particularly, the invention lies in a new safety pilot of the type wherein a fluid filled diaphragm chamber or -bellows and bulb combination is adapted to operate a safety device and sense a flame, respectively, to provide safe operation of a heating system.

One of the objects of this invention is to provide an improved safety pilot of the above mentioned type which provides quick and dependable safety operation as well as being of durable and economical construction.

Another object of the invention is to provide a safety pilot of the abovementioned type wherein a holder for the bulb of the flame sensing unit serves the dual function of supporting the bulb in a substantially non-heat transferring relationship with respect to the burner as well as providing for limited heat dissipation from a capillary tube between the bulb and bellows to limit heat transfer to the capillary tube from the bulb.

A further object of the invention is to provide in a safety pilot a bulb holder formed from sheet metal and being so shaped as to provide a limited heat-conducting connection with the bulb and only slight heat-conducting engagement with the burner which supports it.

Still further objects of the invention will become apparent upon reading the following detailed description of the invention in conjunction with the accompanying drawings wherein:

Figure 1 is an elevational view of the safety pilot with portions thereof broken away;

Figure 2 is an end sectional view taken along line 2-2 in Figure 1 of the drawing;

Figure 3 is a top plan view of the device with the flame sensing bulb and associated parts removed; and

Figure 4 is a plan view of the cut and shaped sheet metal blank and the flame sensing bulb prior to the holder being wrapped around the tubes at each end of the bulb to form the assembly illustrated in Figures 1, 2 and 3.

The invention consists of a burner 11, which is part of the subject matter of a patent application by Raymond P. Flagg et al., Serial No. 290,956, filed May 31, 1952, and entitled Safety Pilot, now Patent No. 2,795,637, a flame sensing unit 12, and a holder 13 for supporting the flame sensing unit with respect to the burner so as to sense the presence or absence of a flame or flames at the burner.

As the burner forms no part of the subject invention, it will be described only in suflicient detail as to make the operation of the invention clear, reference being had to the above mentioned copending application for the details of the burner. Suflice it to say, the burner consists of two burner heads 14 and 15, each having a plurality of orifices 16 therein and receiving gas from a common header member 17 connected to a source of gas supply through a supply pipe 18. The burner heads 14 and 15 'ice are held in assembled but spaced apart relationship by means of end plates 19 and 20, each of which has inwardly directed and spaced arms 19a and 20a, respectively. The plate 20 additionally has laterally and inwardly bent ribs 22 spaced apart the same distance as the arms 20a to provide centering and guiding means for the bulb holder 13. The header 17 has flanges 23 at opposite ends thereof which are spaced apart the same distance as the arms 19a to form therewith a centering or guide means for the opposite side of the holder 13 from'the arms and ribs 20a and 22. The upper end of .theend plate 19 has threaded holes 24 therein for selectively ,receiving a bolt 25 extending through a bracket 26 on a flash tube 27. This provides for the mounting of the flash tube on either side of the burner as well as on the end thereof.

The function of the flash tube 27 is to conduct gas from the main burner 28 to the space over the end orifices in the burner heads adjacent the header 17, so as to ignite the main burner from these pilot burner orifices. The supply pipe 18 has a stepped sleeve 29 thereon that serves to retain the pipe 18 in the header 17.with a wedged fit by hearing against the upper surface of the arms 21 and also provides an abutment in vertical alignment with the outer surface of the header 17 against which the edge of the bulb holder 13 may bear. A set screw 30 bears against the edge of the holder 13 on the line extending between the header 17 and the abutment sleeve 29, to provide a three-point clamping contact between the burner and 'the holder. The pipe 18. bears against the inner end of the slot 21 lying between the arms 19a.

The bulb 12 is formed of approximately a one inch length of a metal tube 31 which is sealed at one of its ends by means of a short length of capillary tubing 32 and connected at its other end by a longer length of capillary tubing 33 to a conventional bellows 34. The bulb, bellows and connecting tubing is preferably filled through the short length of capillary tubing which is sealed by pinching and welding the outer end'thereof. The bellows 34 consists of an outer relatively stiff 'cupshaped member and a relatively flexible inner cup-shaped member to which is connected an actuating stem 35 to be connected to a control device (not shown), such as a switch or valve or actuating mechanism therefor. The bulb, capillary tube, and bellows are preferably completely filled with a volatile fluid, such as mercury or any other suitable high boiling point liquid, so that when a flame of predetermined size, capable of igniting the main burner is present at the burner heads, the fluid in the bulb 31 will be vaporized to the extent necessary to drive liquid mercury from the bulb and to expand the bellows by an amount necessary to operate the control device. r

The bulb holder 13 is made from a sheet of metal by cutting it to the shape shown in Figure 4 and bending the side edges 36 and 37 upwardly between notches 33 and 39 and the outer end of the sheet, to make the holder more rigid and of desired dimensions. The edges 36 are also notched at 40 for the reception of the set screw 30 so as to provide an accurate positioning of the holder in the burner. It will be noted that the notches 38 and 39 also provide, with a large opening 41 in the holder, a relatively small heat conducting strip of metal for con ducting heat from narrow band portions 42 and 43, which are wrapped around the capillary tubes at opposite ends of the bulb 31. Withv this construction of the bulb holder, it is readily apparent that should the blob become defective, it is a relatively simple matter to remove the holder, unwrap the holder from the bulb, replacethe bulb a new bulb, and then reclamp the holder in the burner.

Operation With the invention installed in a heating systermthat is, with the pilot burner 11 and the main burner 28 connected to a suitable source of gas and a bellows unit 34 connected to a suitable control device for supplying the gas to the main burner, the safety pilot is placed in operation by supplying gas to'the burner 11, either by manual operation of the safety control or by some other suitable means. Upon the burner heads becoming ignited,

the flames from the orifices in the burner will play upon the bulb 31 and secondary air for supporting this combustion of the flame will pass upwardly between the holder '13 and the two burner heads to cool the holder 13 below the member 35 to hold the safety control in operating position. The bellows will expand only a predetermined amount, as once all the liquidis expelled from the bulb 31, additional heading of the bulb will not create any appreciable further expansion, as to unduly load or damage the safety device. To prevent the volatilization of the liquid in the capillary tube 33 by heat conduction from the bulb 31, the loop 42 of the holder will conduct heat from the capillary tube 33 adjacent the bulb 31 to the main body portion of the holder and thus dissipate the heat to the secondary air. Upon flame failure, the bulb 31 will quickly cool down due to the small heat storing mass of the bulb and supporting bands, permitting the vapor therein to condense and, thereby permitting the fellows 34 to contract and to cause safety cutoff of the flow of main gas or main and pilot gases.

As modifications may be made in the above described preferred embodiment of the invention, without departing from the spirit thereof, the scope of the invention is to be determined solely from the appended claims.

I claim:

1;. The combination comprising a burner having two "laterally spaced and longitudinally extending burner heads with a plurality of orifices therein, a fluid filled flame sensing bulb, and expansible motor having. a fluid flow connection with said bulb for actuating a device, a heat dissipating bulb holder having a body portion extending substantially vertically between and spaced from said burner heads andthaving narrow upper extensions terminating in loops that engage opposite ends of said bulb for conducting a limited amount of heat from the extreme ends of said bulb to said body portion, and spaced means on said burner for positioningand holding said bulb holder so as to permit said bulb to be heated by flames from most of said orifices but preventing any substantial heat transfer between said burner and holder. 7 i

2. In a safety pilot, the combination comprising a burner having two laterally spaced and longitudinally extending burner heads with a plurality of orifices therein, a fluid filled flame sensing bulb, an expansible motor means for actuating a control, a tube extending from one end of said bulb to said motor means providing fluid flow to and from said bulb and motor means, a heat dissipating bulb holder having a body portion extending substantially vertically between and spaced from said burner heads and having a narrow upper extension terminating in a loop that engages said tube at said one end of said bulb for conducting a limited amount of heat from the extreme end of said bulb and said tube to said body portion, and spaced means on said burner for posiitoning and holding said bulb holder so as to permit said bulb to be heated by flames from most of said orifices but preventing any substantial heat transfer between said burner and bulb holder.

3. In a safety pilot, the combination comprising a burner having two laterally spaced and longitudinally extending burner heads with orifices therein that produce ribbdni shaped flames, a fluid filled flame sensing bulb extending enerally pa al e to said ad an p i e ot means for actuating a safety control, a heat dissipating bulb holder having a body portion extending substantially vertically between and spaced from said burner heads and having a narrow upper extension terminating in a loop that supports an end of said bulb for conducting a limited amount of heat from said end of said bulb to said body portion, a conduit extending between said motor means and said bulb, and spaced means on said burner for positioning and holding said bulb holder so as to permit said bulb to be heated by flames from said orifices but preventing excessive heat transfer between said burner and bulb holder.

4. The combination comprising a burner having a vertically extending body portion and a horizontally extending head with orifice means therein to provide an upwardly directed ribbon-shaped flame, an expansible motor means, a fluid filled flame sensing bulb having a tube extending therefrom to said expansible motor means for actuating a device, a bulb holder having substantial surface area extending upwardly alongside but slightly spaced from said burner for inducing the flow of secondary air over the surface of said holder and to said orifice means, said holder having an extension of small upwardly directed flame, an expansible motor means,

a fluid filled flame sensing bulb extending generally parallel to said head and having a tube extending therefrom to, said expansible motor means for actuating a device, a bulb holder having substantial surface area extending upwardly alongside but slightly spaced from said burner body portion for inducing the flow of secondary air over the surface of said holder and to said orifice means, said bulb holder having an extension of small cross sectional area in engagement with said tube adjacent said bulb for holding said bulb so as to be heated by said burner and for conducting a limited amount of heat from said tube to said bulb holder, and means on said burner for supporting said bulb holder and providing only slight heat-conducting engagement with said bulb holder.

6. The combination comprising a burner having a vertically extending flat body portion with the upper edge thereof having orifice means therein to provide a ribbon-shaped flame, an expansible motor means, a fluid filled flame sensing-bulb having a tube extending from one end thereof to said expansible motor means for actuating a control, a bulb holder having substantial flat surface area extending alongside but slightly spaced from said burner for inducing the flow of secondary air over the surface-of said holder and to said orifice means, said holder having an extension of small cross sectional area above said burner and in engagement with said tube adjacent saidbulb' for holding said bulb so as to be heated by said burner and for conducting a limited amount of heat from said tube to said holder, and means on said burner for supporting said holder.

References Citedin the file of this patent UNITED STATES PATENTS 2,627,911 McCarty et al Feb. 10, 1953 2,640,313 Cobb June 2, 1953 2,670,394 West Feb. 23, 1954 

